This invention relates to phosphorus salts of dispersant viscosity improvers and lubricating compositions and concentrates containing such salts.
Dispersant viscosity improvers are used in lubricating compositions to control the viscosity decrease of the lubricating oils under increasing temperatures. Additionally, these materials have components which improve the oil""s ability to suspend or xe2x80x9cdispersexe2x80x9d impurities in the oil. The dispersing of the impurities prevents them from depositing on the surface of lubricated parts. Polyacrylates, especially polymethacrylate ester polymers, are well known and widely used as viscosity improvers. When these materials have a nitrogen containing monomer, they act as a multifunctional additives providing viscosity improving properties as well as dispersant properties to the lubricating compositions.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are known in the art. Such products are described in numerous publications including C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp (1978), pp 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
Phosphorus containing antiwear agents have been used to prevent adverse wear to metal surfaces of equipment. The phosphorus antiwear agents act to help prevent adverse metal to metal contact.
It is desirable to have a multifunctional additive that provides the benefits of the dispersant viscosity improvers as well as the phosphorus containing antiwear agents.
This invention relates to a lubricating composition comprising a major amount of an oil of lubricating viscosity and a minor amount of a salt of at least one nitrogen containing polyacrylate and at least one phosphorus acid ester. The invention also relates to lubricating compositions and concentrates containing the same. The present phosphorus salts of the nitrogen containing copolymers provide improved dispersant, viscosity improver and antiwear properties to lubricating compositions. In particular, the salts provide improved viscosity temperature characteristics in finished fluids. The salts also provide improved thermal stability of the lubricating compositions.
As used herein, the terms xe2x80x9chydrocarbonxe2x80x9d, xe2x80x9chydrocarbylxe2x80x9d or xe2x80x9chydrocarbon basedxe2x80x9d mean that the group being described has predominantly hydrocarbon character within the context of this invention. These include groups that are purely hydrocarbon in nature, that is, they contain only carbon and hydrogen. They may also include groups containing substituents or atoms which do not alter the predominantly hydrocarbon character of the group. Such substituents may include halo-, alkoxy-, nitro-, etc. These groups also may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen and oxygen. Therefore, while remaining predominantly hydrocarbon in character within the context of this invention, these groups may contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms.
In general, no more than about three non-hydrocarbon substituents or hetero atoms, and preferably no more than one, will be present for every 10 carbon atoms in the hydrocarbon or hydrocarbon based groups. Most preferably, the groups are purely hydrocarbon in nature, that is they are essentially free of atoms other than carbon and hydrogen.
As used herein, the terms xe2x80x9cacrylatexe2x80x9d and xe2x80x9cacrylamidexe2x80x9d includes their alkyl substituted versions, such as lower alkyl acrylates and lower alkyl acrylamides, and especially, methacrylates and methacrylamides. Lower alkyl refers to groups containing 8 or less carbon atoms.
The nitrogen-containing polymers of this invention may be prepared by several different processes. In one embodiment, the nitrogen-containing polymer is obtained by reacting, together, the acrylate ester monomers and the nitrogen-containing monomer. In another embodiment, the nitrogen-containing monomer is grafted onto a preformed acrylate copolymer backbone.
The nitrogen containing polymers generally have weight average molecular weight (Mw) ranging from about 10,000 to about 350,000 or from about 12,000 to about 200,000 or from about 15,000 to about 150,000 or from about 20,000 to about 120,000. Here and elsewhere in the specification and claims range and ratio limits may be combined. Polydispersity of the nitrogen containing polymers (abbreviated PDI for polydispersity index) values (Mw/Mn), where Mn denotes number average molecular weight, range from about 1.2 to about 5, or from about 2 to about 4.
Molecular weights of polymers are determined using well-known methods described in the literature. Examples of procedures for determining molecular weights are gel permeation chromatography (also known as size-exclusion chromatography) and vapor phase osmometry.
The nitrogen containing polymers of the present invention are derived from a majority of acrylate ester monomers. In one embodiment, the ester groups of the acrylate monomers independently contain from about 1 to about 30 carbon atoms, or from about 4 to about 24 carbon atoms. The acrylate monomers are generally derived by esterifying acrylic or methacrylic acid with one or more alcohols. Useful alcohols include methyl alcohol, ethyl alcohol, butyl alcohol, octyl alcohol, iso-octyl alcohol, isodecyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, pentadecyl alcohol, palmityl alcohol, stearyl alcohol and the like. The additional alcohols and the acrylate monomers derived therefrom may be used to make the majority of the polymer. These monomers may be used alone or in combination. The alcohols may be reacted with acrylic acid or methacrylic acid to form the desirable acrylates or methacrylates.
The acrylate ester monomers can be prepared by conventional methods well-known to those of skill in the art.
In one embodiment, the nitrogen-containing polymers are derived from (a) from about 5% to about 75% by weight, or from about 30% to about 60% by weight of alkyl acrylate ester monomers containing from 1 to 11 carbon atoms in the alkyl group and (b) from about 25% to about 95% by weight, or from about 40% to about 70% by weight of alkyl acrylate ester monomers containing from 12 to about 24 carbon atoms in the alkyl group. Alkyl methacrylate esters are particularly useful monomers. In another embodiment, monomer (a) comprises at least 5% by weight of alkyl acrylate esters having from 4 to 11 carbon atoms in the alkyl group. In another embodiment, monomer (a) comprises from about 10% to about 40% by weight alkyl acrylate esters having from 1 to 4 carbon atoms in the alkyl group. In still another embodiment, monomer (a) comprises from about 60% to about 90% by weight of alkyl acrylate esters having from 9 to 11 carbon atoms in the alkyl group.
In another embodiment, the nitrogen containing polymers are derived from a mixture of alkyl methacrylate ester monomers containing, (a) from about 9 to about 25 carbon atoms in the ester group, or from about 13 to about 19 carbon atoms, or to about 16 carbon atoms, and (b) from about 7 to about 12 carbon atoms in the ester group, or from about 9 to about 12 carbon atoms, or 9 carbon atoms. In one embodiment, the polymer is derived from ester (a) and (b) and at least one monomer selected from the group consisting of methacrylic acid esters containing from 2 to about 8 carbon in the ester group atoms and which are different from methacrylic acid esters (a) and (b). Typically, the mole ratio of esters (a) to esters (b) in the copolymer ranges from about 95:5 to about 35:65, often from about 90:10 to about 60:40, and frequently from about 80:20 to about 50:50. In one embodiment, ester (b) are branched.
As noted herein above, the ester alkyl group is generally derived from an alcohol. Alcohols which are useful for preparing ester (a) contain from about 8 to about 24 carbon atoms, or from about 12 to about 15 carbon atoms. Mixtures of alcohols are commercially available and are frequently useful. The alcohols used to prepare ester (a) may be linear or branched. In one embodiment, from about 2 to about 65% of the alcohols are branched, frequently from about 5 to about 60% are branched. Examples of alcohols useful to prepare ester (a) include n-octanol, n-decanol, n- and branched-C12, C15, C16, and C22 alcohols, mixtures of alcohols, e.g., C12-15 alcohols available under the tradenames Dobanol 25, Neodol 25, Lial 125, and Alchem 125, which have varying degrees of branching, for example from about 5% to about 50% branching, or even more, and Alfol 1214, which is substantially linear. In one embodiment, the ester groups in ester (a) contain branched alkyl groups. Often from about 2 to about 65%, frequently from about 5 to about 60% of the ester groups contain branched alkyl groups.
Alcohols which are useful for preparing ester (b) contain from 6 to about 11 carbon atoms, or from 8 to about 11, or 8 carbon atoms. These alcohols have a 2-(C1-4 alkyl) substituent, namely, methyl, ethyl, or any isomer of propyl and butyl. Examples of alcohols useful for preparing ester (b) include 2-methylheptanol, 2-methyldecanol, 2-ethylpentanol, 2-ethylhexanol, 2-ethyl nonanol, 2-propyl heptanol, -2-butyl heptanol, etc. Especially useful is 2-ethylhexanol. As noted, the ester (b) has 2-(C1-4 alkyl)-substituents. The C1-4 alkyl substituents may be methyl, ethyl, and any isomers of propyl and butyl. A useful 2-alkyl substituent is ethyl.
(C) The Nitrogen-Containing Monomer
The nitrogen-containing polymers of this invention are derived from a nitrogen containing monomer. Typically the nitrogen containing monomers are present in an amount from about 0.1% to about 20%, or from about 0.5% to about 5% by weight, or from about 1.5% to about 2.5% by weight. In one embodiment, the nitrogen containing monomer is present in an amount from about 0.2, often from about 1 mole %, up to about 20 mole %, more often up to about 8 mole %, of groups derived from monomer (c).
The nitrogen containing monomer may be any monomer that is capable of copolymerizing with acrylate monomers or is capable of being grafted onto polyacrylate polymers. The nitrogen containing monomers include vinyl substituted nitrogen heterocyclic monomers, dialkylaminoalkyl acrylate monomers, dialkylaminoalkyl acrylamide monomers, tertiary-acrylamides and the like.
Useful nitrogen containing monomers include vinyl substituted nitrogen heterocyclic monomers, for example vinyl pyridine and N-vinyl-substituted nitrogen heterocyclic monomers, for example, N-vinyl imidazole, N-vinyl pyrrolidinone, and N-vinyl, caprolactam; dialkylaminoalkyl acrylate and methacrylate monomers, for example N,N-dialkylaminoalkyl acrylates, dimethylaminoethyl methacrylate or dimethylamine propyl methacrylate; dialkylaminoalkyl acrylamide and methacrylamide monomers, for example di-lower alkylaminoalkylacrylamide, especially where each alkyl or aminoalkyl group contains from 1 to about 8, or from 1 to 3 carbon atoms, for example N,N-di lower alkyl, especially, dimethylaminopropylacrylamide; N-tertiary alkyl acrylamides and corresponding methacrylamides, for example tertiary butyl acrylamide, vinyl substituted amines and the like.
The nitrogen containing polymers of may be prepared in the presence of a diluent. A diluent may also be added to a substantially diluent-free copolymer, usually by dissolving or dispersing the substantially diluent-free polymer in an appropriate diluent. In one embodiment, the diluent is a mineral oil, such as, for example, hydrotreated naphthenic oil, or a synthetic oil, such as ester type oils, polyolefin oligomers or alkylated benzenes. Useful diluents are naphthenic oils, hydrotreated naphthenic oils, and alkylated aromatics, particularly alkylated benzenes having at least one alkyl group containing from about 8 to about 24 carbon atoms, or from 12 to about 18 carbon atoms. Especially useful are hydrotreated naphthenic oils, examples being Risella G-07, Cross Oil Co.""s L-40, a 40 neutral hydrotreated naphthenic oil and L-60, which is a 60 neutral oil.
The diluent-containing polymers are referred to herein as additive concentrates. Such additive concentrates are then added, along with other desirable performance-improving additives, to an oil of lubricating viscosity to prepare the finished lubricant composition. In one embodiment, the additive concentrates comprise from about 25% to about 90% by weight of copolymer, or from 35% to about 80% by weight, and from about 10% to about 75% by weight of diluent, or from about 20% to about 65% by weight of diluent.
The copolymers of this invention may be prepared by several different techniques. In one embodiment, the acrylate ester monomers and nitrogen-containing monomer are reacted together. In another embodiment, the acrylate esters are reacted to form an acrylate ester copolymer backbone onto which is grafted a nitrogen-containing monomer. In still another embodiment, a mixture of acrylate and nitrogen-containing monomers may be grafted onto a preformed acrylate ester polymer backbone.
In the first embodiment, a mixture of monomers is charged to a reactor together with, if desired, diluent and again, if desired, chain transfer agent. The materials are stirred under a nitrogen atmosphere. Subsequently, a polymerization initiator is added and the materials are heated to reaction temperature. The reaction is continued until the desired degree of polymerization is attained.
In an alternative embodiment, the monomers are polymerized incrementally. A mixture of monomers together with a polymerization initiator is prepared. A portion, typically about 20% to about 40%, more often about 33%, of the mixture, is charged to a reactor with the balance being placed in an addition vessel. The reactants are heated under a nitrogen atmosphere until an exothermic reaction is noted. When the exothermic reaction begins to subside, addition of the balance of the monomer-initiator mixture is begun, while maintaining, via heating or cooling, as needed, the desired reaction temperature.
In the second embodiment, the acrylate monomers are polymerized, then the grafting of the nitrogen-containing monomer onto the preformed acrylate ester copolymer is accomplished. A mixture of additional acrylate monomers together with nitrogen-containing monomer may be grafted onto the preformed acrylate ester polymer.
The entire charge of the nitrogen containing monomer may be present at the start of the polymerization process. Alternatively, the nitrogen containing monomer may be added to the already prepared polyacrylate either gradually or incrementally. In the grafting process, additional initiator is usually employed during the grafting step. In either process, additional initiators may be added during processing.
Polymerization can take place under a variety of conditions, among which are bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization and nonaqueous dispersion techniques.
To prepare the copolymers constituting the dispersant viscosity improvers in accordance with the invention it is possible to make use of the conventional methods of radical copolymerization. These methods include free-radical initiated polymerization employing azo compounds or peroxides, photochemical and radiation initiated methods. Molecular weights of the polymers can be controlled employing a number of techniques including choice of initiator, reaction temperature, concentration of monomers and solvent type. Chain transfer agents can also be used. The products of the present invention are generally prepared at temperatures ranging from about 60xc2x0 C. to about 140xc2x0 C., or from about 80xc2x0 C. to about 120xc2x0 C.
Another useful means for preparing the copolymers of this invention is to employ known in the art high energy mechanical mixing devices. These include roll mills, ball mills or extruders. Of these, extruders are preferred since the comonomers can be fed to the feed hopper in any desired fashion.